[alsa-devel] Duplicate wake-ups in pcm_lib.c

Jaroslav Kysela perex at perex.cz
Mon Jan 11 19:51:29 CET 2010

On Mon, 11 Jan 2010, pl bossart wrote:

>> The improved and more clean fix in now in my tree:
>> http://git.alsa-project.org/?p=alsa-kernel.git;a=commitdiff;h=1250932e48d3b698415b1f04775433cf1da688d6
> The race condition is definitely gone. However I still see a NULL
> event in snd_pcm_playback_poll() in pcm_native.c.

> [13312.755305] ALSA: null poll event, avail 265 avail_min 8192
> I couldn't figure out who generates this null event, and even better
> it does not show in the report printed by my test app. I am somewhat
> lost here as to how snd_pcm_playback_poll works.

Note that do_poll() in linux/fs/select.c first checks all given fds
if there's an event. So probably the userspace just called poll() for a 
reason in different timing than sound one (processing event from another 
fd or so). I believe it's normal behaviour.


Jaroslav Kysela <perex at perex.cz>
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.

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